FIG. 1 is a diagram showing a prior method for single wire transmission, wherein a signal is transmitted from a transmitting end Tx to a receiving end Rx. The signal includes a start bit, data with a predetermined length (the data can be a command code, a numeric code, or a command code combined with a numeric code), and an end bit. As the arrow in FIG. 1 shows, when the start bit is received at the receiving end Rx, a clock signal is generated synchronously with the rising edge of the start bit. Then the data is received, and the length of the data is counted according to the clock signals. The length of the data should comply with a communication protocol predetermined between the transmitting end Tx and the receiving end Rx. The above method belongs to synchronized transmission, because the transmitting end Tx has to transmit data synchronously with the clock frequency of the receiving end Rx.
A shortcoming of the above single wire transmission is that the transmitting end Tx has to know the clock frequency of the receiving end Rx in advance. Furthermore, the transmitting end Tx has to properly arrange set-up time and hold time of the transmitted signals to make sure that the data can be received correctly.
FIG. 2 is a diagram showing a conventional arrangement for tri-state single wire transmission, wherein there are three states for a data signal, including “0”, “1”, and “T” (third-state).
U.S. patent publication No. 2003/0219004 discloses a method for single wire transmission using tri-state signals. One of the three states may be used as a synchronization bit, and the receiving end can generate clock signals according to the synchronization bits for synchronization with the transmitting end. This method also belongs to synchronized transmission, but is different from the previous method in that it uses tri-state signals, and that the synchronization is achieved by the receiving end following the synchronization protocol defined by the synchronization bits, instead of the transmitting end following the predefined synchronization protocol.
In the above-mentioned prior methods, clock synchronization is a “must”, either by the transmitting end following the predefined synchronization protocol, or by the receiving end following the synchronization protocol defined by the synchronization bits. Either way, it creates a burden for circuit design or communication protocol.
However, if clock synchronization is not established, it is difficult to identify signals received at the receiving end.
In view of the foregoing, it is desired to provide a method for single wire transmission which does not require clock synchronization between a transmitting end and a receiving end, wherein signals received at the receiving end can be identified clearly.